The invention relates to a method for efficiently preparing biogas by taking pennisetum alopecuroides as a raw material and particularly relates to a new method for increasing the fermentation yield of pennisetum alopecuroides biogas by taking pennisetum alopecuroides as a raw material and adopting the assistant new technology of high-voltage pulsed electric field, belonging to the field of biological fermentation. In the invention, resource utilization of pennisetum alopecuroides is fully realized, and the types of energy plants are effectively expanded; meanwhile, by introducing the new technology of high-voltage pulsed electric field into the pennisetum alopecuroides biogas fermentation technology, wall-breaking treatment of the pennisetum alopecuroides fermentation material is realized, the lignocellulose structure in the pennisetum alopecuroides is effectively damaged, and the utilization rate and biogas yield of pennisetum alopecuroides fermentation are effectively increased; and moreover, the fermentation technology of the pennisetum alopecuroides fermentation material is overall adjusted and optimized, thus the fermentation process is more reasonable and stable, the utilization rate and biogas yield of pennisetum alopecuroides fermentation are further increased, the biogas production cycle is shortened, the operation is simple, and the controllability and practicability are high.